This invention relates to a gear shift controller for an automatic transmission with a one-way clutch interposed in at least one gear train of those which correspond to each of a plurality of change steps (hereinafter referred to as gears), which comprises actuating only the gear train in which the one-way clutch is interposed in an idling state regardless of normal gear shift operation.
In most cases, generally, where a car in top gear slows to adjust the distance between itself and another car or runs down a gentle downward slope, the driver lifts off the throttle to coast. In such a case, it is preferable that the transmission be in neutral to save fuel, an important concern among drivers today.
In a car operating with an automatic transmission, when it coasts in the D-range, or in top gear, the gear shift is kept, in most cases, at a top gear according to a control program set beforehand, and if so, fuel consumption can be saved somewhat by the sliding action of a torque converter. However, the engine is still idling, thus the fuel consumption cannot be optimized. Moreover, it is very troublesome to manually shift the transmission to the N-range or neutral gear whenever the car is coasting, thus destroying the essential convenience of the automatic transmission.
On the other hand, in a transmission with a top gear ratio which is an "overdrive" (that is, the ratio is less than 1) engine braking when in top gear is not very effective, and particularly in the case of a transmission with a torque converter, the effect is almost nil. However, in the case of a transmission with a torque converter, there is normally a gear having an engine braking effect one step lower than the top gear, therefore the particular gear can be used for engine braking. For a driver who wants to have engine braking at the time of gear shift on the top gear despite the minor effect of the engine braking, it is desirable that the engine braking be available at the time of the gear shift on the top gear as occasion demands.